1. Field of the Invention
The present invention relates generally to an airfoil management device and more particularly to the use of passive porosity in combination with (controlled transference and seepage of air through the skin of various regions of airfoils for use as lift and drag management devices.
2. Description of the Prior Art
Conventional non-porous airfoils typically utilize various mechanical structures, such as spoilers and associated structural and actuation hardware, in order to alter, vary and control the lift on an airfoil. Spoilers are typically comprised of at least one structural member which is movably connected to an airfoil, with various types of mechanical hardware, such that the structural member may be hydraulically, pneumatically, or otherwise mechanically raised into the airstream on at least one side of an airfoil in order to interrupt the air flow over the respective surface of the airfoil. Such devices are used to achieve a variety of objectives including, for example, to provide roll control, direct lift control, increased drag to facilitate greater engine power requirements (some engines have improved performance characteristics when operated at increased power levels), a reduction in altitude gain during aircraft landing (sometimes referred to as flap anti-ballooning), and to increase drag and reduce velocity (sometimes referred to as "air brakes").
Conventional hydraulic, pneumatic, and other mechanical devices (such as spoilers), including the structural and actuation hardware related thereto, utilized to alter, vary and control lift are subjected to various static and dynamic forces, loads, pressures, stresses, strain, wear, and fatigue which result in reducing the life and accelerated failure of the various components. Of course, as the structural and actuation hardware are fastened or otherwise affixed to the airfoil itself, the static and dynamic forces, loads, pressures, stresses, and strains which occur in or upon the structural components and actuation hardware are transferred or otherwise transmitted to portions of the airfoil itself resulting in wear, fatigue and a reduction in the useful life of the wing structure itself. Reducing or eliminating such forces and wear upon such components, and upon wings in general, would serve to increase the reliability, useful life, and safety of any aircraft, vehicles, or other devices which utilize conventional lift control mechanisms.
Conventional mechanical lift control mechanisms, such as spoilers, and their related structural components and actuation hardware, utilize a substantial amount of beneficial area and mass. The mass attributable to conventional mechanical lift control mechanisms result in decreased usable space, heavier crafts, decreased fuel efficiency, and increased loads. In airfoil applications, the efficient utilization of useable area and mass is extremely important. If the amount of area and mass required to employ lift control mechanisms, such as spoilers, could be partially or totally eliminated, such area and mass could be employed for other useful purposes such as, for example, additional or increased passenger or cargo capacity, fuel storage, instrumentation, or armament storage.
Through the use of passive porosity and the controlled seepage and transference of air through one or more surfaces on various regions of an airfoil, the present invention partially or completely eliminates the need for conventional mechanical lift and drag control mechanisms, such as spoilers, and most of the associated structures, actuation devices, support hardware, hydraulic systems, and other related components thereto, thereby increasing the amount of usable area and space on and in an airfoil, decreasing the number of required moving parts, decreasing the amount of mass necessary to achieve the results previously only performed by mechanical structures such as spoilers, and eliminating the various static and dynamic forces, loads, pressures, stresses, strain, wear, and fatigue which result from conventional mechanical lift control mechanisms. Additionally, as the present invention will partially or completely eliminate the mechanical disruption of airflow as accomplished by conventional spoilers, thereby partially or completely eliminating the need to physically maneuver mechanical spoiler structures into an airstream, the present invention will result in substantially improved acoustic signatures and decreased reflective surfaces.
The general use of porous skin regions on airfoils is disclosed in U.S. Pat. Nos. 5,167,387, 4,575,030, and 4,726,548. In an attempt to improve lift and drag characteristics at subcritical and supercritical conditions, U.S. Pat. No. 5,167,387 uses porous airfoil skin surfaces to vent air pressure from the leading edge region to the trailing edge region of an airfoil in order to alter the effective airfoil thickness. U.S. Pat. No. 4,575,030 uses active suction mechanisms in connection with porous airfoil skin surfaces in an attempt to control the laminar flow over an aircraft wing. U.S. Pat. No. 4,726,548 uses porous airfoil skin surfaces in an effort to draw boundary layer air into an airfoil and then evacuate such air at the end of the airfoil in order to improve drag characteristics. U.S. Pat. No. 2,077,071 discloses a boundary layer control mechanism for airfoils.
The disadvantages of the prior art are overcome by the present invention which uses passive porosity in combination with controlled seepage and transference of air through the skin on various regions of an airfoil for use as a lift and drag management device thereby partially or completely eliminating conventional mechanical components and systems for altering, varying and controlling lift and drag or enhancing the capabilities of the airfoil. Additionally, unlike the prior art, the present invention does not require that the air be vented from one plenum chamber to another, rather, the present invention has the unique ability to effect and control lift and drag on an airfoil by controlling the seepage and transference of air through one or more porous skin regions into and out of one or more corresponding plenum cavities. The present invention does not require that the air in one plenum cavity which is associated with a porous region be able to fluidly communicate with the air or air pressure in any other plenum cavity or any other porous region. The present lift management invention has the unexpected result of allowing for a decreased amount of moving parts, improved airfoil acoustic signatures, improved efficiency and reliability, increased performance characteristics, a decrease in the amount of mass necessary to achieve lift and drag management, and the elimination or reduction of separate control surfaces and related hardware required to achieve lift and drag management by conventional means. Further advantages of the present invention will be recognized by those skilled in the art.